1. Field of the Invention
This invention relates to a method of detecting a motion picture (as opposed to a still picture) in an interlaced-progressive scanning converter. Specifically, it relates to a method of detecting a rapid movement at a slight error, using the correlation between pixels above and below a pixel to be interpolated. The present application is based upon Korean Application No. 67758/1995, which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, an interlaced-progressive scanning converter indicates an apparatus for changing an interlaced-scanned signal into a progressive-scanned signal. Such interlaced-progressive scanning converter is a signal processing unit for preventing the deterioration of vertical resolution, flicker of a scanning line, and flicker of a broader area which are caused by a conventional television system's interlaced scanning. There are several methods used, such as a dual scanning, an interpolation using two neighboring scanning lines, and a repetition of the value of a field just before the present field. Picture quality can also be improved by using a motion compensating method.
A general interlaced-progressive scanning converter has a structure shown in FIG. 1. As shown in FIG. 1, a motion picture detecting unit 110 detects a motion picture after comparing the pixels above and below a pixel to be interpolated in a field which is being scanned, or after comparing a previously scanned field and a field which will be scanned next. Field memories 112 and 114 temporarily store one field of picture signal externally input through a video input port and buffer it according to the order of input of the data. An interpolation circuit 116 interpolates the picture signal which will be scanned in units of a pixel, under the control of the motion picture detecting unit 110.
In FIG. 2, characters X, A, and B each represent pixels of the field being presently scanned. X is the pixel which will be interpolated. A and B are the pixels above and below, respectively, the pixel to be interpolated. C represents the pixel of the previously scanned field, and D represents the pixel of the field which will be scanned after the present field, C and D both being located at positions in their respective fields corresponding to the field position of pixel X. One frame is composed of two fields, so that C and D do not belong to the same frame.
With reference to FIGS. 1 and 2, a conventional interpolation after detecting the motion picture will be explained below.
Pixels A, B, C, and D shown in FIG. 2 are utilized for interpolating pixel X. The method using pixels A, B, C, and D can be described, using the following formulas. If .vertline.C-D.vertline., that is, the difference between the preceding and succeeding frames, is smaller than a first threshold th1, it is decided that there is no movement between frames. If the difference between a value ##EQU1## in case of temporal interpolation and a value ##EQU2## in case of spatial interpolation is smaller than th2, it is decided that there is no movement between fields. In other words, if the differences between the present field value ##EQU3## and the preceding or succeeding field value ##EQU4## are respectively are smaller than a second threshold th2, it is decided that there is no movement between fields. Consequently, a picture is judged to be a stationary picture if the first and second formulas below are met. ##EQU5##
Generally, th1 and th2 are determined when products are manufactured. They represent decision coefficients which are standards for detecting the motion picture.
When the picture is detected to be in motion by using the above formulas, the interpolation is performed by a method of ##EQU6## using the pixels A and B in the same field.
When the picture is detected to be stationary by using the above formulas, the interpolation is performed with C, D or ##EQU7## using the preceding field pixel C and the succeeding field pixel D.
In the above detecting methods, the decision coefficient th2 is generally established as being larger than th1. The established decision coefficient th2 is a fixed value, which makes it difficult to properly distinguish the movement between fields. If the decision coefficient th2 is established as a small value, too many stationary pictures are judged as being motion pictures. If the decision coefficient th2 is established as too large a value, it is difficult to accurately distinguish the movement between fields, so that a problem of motion blurring occurs in a finally interpolated picture.